This invention relates generally to radio frequency antennas and more particularly to radio frequency lens type radio frequency antennas.
As is known in the art, an antenna may be arranged so that it produces a plurality of simultaneously existing beams of radio frequency energy with each one of such beams having the gain and bandwidth of the entire antenna aperture. According to the art, a desired number of simultaneous beams may be obtained by connecting each one of a plurality of antenna elements in an array thereof through a constrained electrical path to a plurality of beam ports, the constrained electrical path being made up of an electromagnetic lens which equalizes the time delay of the electromagnetic energy between any given one of a number of beam ports and all points on corresponding planar wave fronts of transmitted energy. Any one of a variety of known electromagnetic lenses may be used. One such lens is a so called "Rotman" lens described in a paper entitled "Wide Angle Microwave Lens for Line Source Applications" by W. Rotman and R. F. Turner (Transactions of Antennas and Propagation, pp. 623-632, published in November 1963 by the Institute of Electrical and Electronics Engineers, Inc., New York, New York). Another such lens is described in U.S. Pat. No. 3,761,936 issued Sept. 25, 1973, entitled "Multi-Beam Array Antenna" inventors Donald H. Archer, Robert J. Prickett and Curtis P. Hartwig and assigned to the same assignee as the present invention. With either one of such lenses, a lens shaped, parallel plate region is provided with a plurality of beam ports and a plurality of array ports being disposed about opposing peripheral portions of the region. Each one of the array ports is coupled to a corresponding one antenna element in an array of antenna elements and each one of the beam ports is associated with a corresponding one of a plurality of differently directed, relatively narrow beams of radio frequency energy.
When used as a transmitting antenna system, an amplifier, typically a travelling wave tube (TWT) amplifier, is coupled between each one of the array ports and a corresponding one of the antenna elements. While such arrangement thus provides a plurality of differently directed, relatively narrow transmitted beams, in some applications it is desirable to transmit a broad or "flood" beam. Such flood beams have been produced by by-passing the parallel plate lens and feeding the radio frequency signal to only a single antenna element via the input to the amplifier feeding such single antenna element. With such arrangement, however, the system radiated power efficiency suffers because the power from the other amplifiers in the system is not used in producing the "flood" beam.